n. [ Cyclo- + -oid: cf. F. cycloïde. ] (Geom.) A curve generated by a point in the plane of a circle when the circle is rolled along a straight line, keeping always in the same plane. [ 1913 Webster ]

☞ The common cycloid is the curve described when the generating point (p) is on the circumference of the generating circle; the curtate cycloid, when that point lies without the circumference; the prolate or inflected cycloid, when the generating point (p) lies within that circumference. [ 1913 Webster ]

a. (Zool.) Of or pertaining to the Cycloidei. [ 1913 Webster ]

Cycloid scale (Zool.), a fish scale which is thin and shows concentric lines of growth, without serrations on the margin. [ 1913 Webster ]

n. (Zool.) One of the Cycloidei. [ 1913 Webster ]

a. Pertaining to, or resembling, a cycloid; as, the cycloidal space is the space contained between a cycloid and its base. [ 1913 Webster ]

Cycloidal engine. See Geometric lathe. [ 1913 Webster ]

‖n. pl. [ NL., fr. Gr. ky`klos circle + -oid. ] (Zool.) An order of fishes, formerly proposed by Agassiz, for those with thin, smooth scales, destitute of marginal spines, as the herring and salmon. The group is now regarded as artificial. [ 1913 Webster ]

a. & n. (Zool.) Same as 2d and 3d Cycloid. [ 1913 Webster ]